A new study has shown that pistachio nuts, eaten as part of a healthy diet, can increase the levels of antioxidants in the blood of adults with high cholesterol.
"Our previous study showed the benefits of pistachios in lowering lipids and lipoproteins, which are a risk factor for heart disease. This new study shows an additional effect of pistachios so now there are multiple health benefits of eating pistachios." said Penny Kris-Etherton, distinguished professor of nutrition, Penn State.
The researchers note that "pistachios are high in lutein, beta-carotene and gamma-tocopherol relative to other nuts; however, studies of the effects of pistachios on oxidative status are lacking."
Beta-carotene is the precursor to vitamin A and gamma-tocopherol is a common form of vitamin E. Lutein is found in dark green leafy vegetables and is important in vision and healthy skin. All three compounds are oil soluble vitamins.
Antioxidants are of interest because oxidized low-density lipoproteins (LDL) are implicated in inflammation and plaque buildup inside blood vessels. Antioxidants should prevent LDLs from oxidizing, migrating into the blood vessel walls and causing inflammation.
The researchers conducted a randomized, crossover design, controlled feeding experiment to test the effects of pistachios on antioxidant levels when added to a heart healthy moderate-fat diet. Controlled feeding experiments provide all the food eaten by study subjects for the duration of the study period.
The participants began the study by eating a typical American diet consisting of 35 percent total fat and 11 percent saturated fat for two weeks.
They then tested three diets for four weeks each with about a two-week break between each diet. All three diets were variations on the Step I Diet, a cholesterol-lowering diet in general use. The diets included, as a control, a Step I Diet with no pistachios and about 25 percent total fat and 8 percent saturated fat.
The pistachio-enhanced diets were Step I Diets with 10 and 20 percent of the energy supplied by pistachio nuts, respectively. The 10 percent pistachio diet had 30 percent total fat and 8 percent saturated fat and the 20 percent pistachio diet had 34 percent total fat and 8 percent saturated fat.
The actual amounts of pistachios included in each diet were 1.5 ounces and 3 ounces for the 10 and 20 percent diets, respectively.
Both pistachio diets produced higher blood serum levels of beta-carotene, lutein and gamma-tocopherol than the typical American diet. Compared to the pistachio free Step I Diet, the pistachio-enhanced diets produced greater blood plasma levels of lutein and gamma-tocopherol. After eating both pistachio-enriched diets, the participants had lower oxidized-LDL concentrations in their blood than after the control Step I Diet.
When the researchers controlled for the change in LDL-cholesterol produced by the pistachio-enhanced diets, increases in beta-carotene and gamma-tocopherol were still associated with decreased oxidized-LDL for the 3-ounce pistachio-enhanced diet.
"Our results suggest that a heart-healthy diet including pistachios contributes to a decrease in serum oxidized-LDL levels, in part through cholesterol lowering, and also due to an added benefit of the antioxidants in the pistachios," said Kris-Etherton.
The study has been published in the Journal of Nutrition.